JP2011529243A - Silicon-containing lithium lanthanum titanate composite solid electrolyte material and method for producing the same - Google Patents

Abstract

  The present invention relates to a silicon-containing lithium lanthanum titanate composite solid electrolyte material in which amorphous Si or Si compounds are present at grain boundaries between crystal grains, and a method for producing the same, and belongs to the field of lithium ion batteries. A feature of the present invention is that amorphous Si or Si compound (2) is present at the grain boundary between lithium lanthanum titanate crystal particles (1), and this amorphous Si or Si compound ( 2) is introduced into the grain boundary, and in this wet chemical method, an inexpensive organosilicic compound is used as an additive in the lithium lanthanum titanate solid electrolyte material, and the silicon content is converted to Si The silicon-containing lithium lanthanum titanate composite solid electrolyte material can be obtained by sintering when the mass ratio to the lithium lanthanum titanate is 0.27% to 1.35%. It is in a point that can be done. Since its grain boundary conductivity is significantly improved, the overall conductivity is improved, and the process of the experimental method is simple and easy to operate, and the experimental period is greatly shortened, the synthesis temperature is lowered, Reduce energy consumption and production costs.

Description

  The present invention belongs to the field of lithium ion batteries, and relates to a highly safe silicon-containing lithium lanthanum titanate composite solid electrolyte material for lithium ion batteries and a method for producing the same.

  As energy and environmental pressures increase, developing a clean and highly efficient transportation alternative to conventional vehicles fueled by gasoline and light oil to reduce dependence on oil and pollution to the environment It has become a strategic policy direction for the development of the automobile industry, established around the world. With the development of new energy vehicles, higher demands are being made on the storage of motive energy. As a power battery, the battery needs to have smaller dimensions, lighter weight and higher safety. Lithium ion batteries are considered the best choice for power batteries in future new energy vehicles because lithium ion batteries are superior to other secondary batteries due to their high operating voltage, mass density and energy density .

  Currently, all of the new energy concept cars deployed by major automakers around the world use lithium-ion batteries as their power batteries. It is rare to see. The advantage of liquid electrolytes is that they have high conductivity, but this type of battery requires strict sealing to ensure that the liquid electrolyte does not leak out, limiting the reduction in battery volume due to sealing requirements. In addition to the fact that most of the liquid or gel electrolytes are flammable organic substances, the battery may burn under conditions that receive heat or generate chemical reactions with the electrodes. .

However, since solid inorganic electrolytes can just compensate for the drawbacks of liquid or gel electrolytes, those skilled in the art are largely involved in the research and development of solid electrolytes. However, the biggest barrier in the practical application of solid inorganic electrolytes is that the electrical conductivity used is very low and does not greatly meet commercial demands (for example, electrical conductivity reaching 10 ⁻³ S / cm).

At present, among the many inorganic solid electrolytes discovered by those skilled in the art, lithium lanthanum titanate (LLTO) whose conductivity is relatively close to the commercial level is Li _3x La _{2 / 3-3- x} TiO ₃ (0 <x <0.16). The crystal grain conductivity has already reached 10 ⁻³ S / cm at room temperature, but its grain boundary conductivity is below 10 ⁻⁵ S / cm, which reduces the conductivity of LLTO. Therefore, it cannot meet practical requirements. Therefore, the improvement and improvement of grain boundary conductivity is the most direct and effective way to improve the conductivity of this solid oxide lithium ion conductor, which is the use of oxide solid electrolyte. It is also a bottleneck problem.

  The present invention provides a silicon-containing lithium lanthanum titanate composite solid electrolyte material that effectively improves the conductivity of LLTO and is promising for use in high efficiency power lithium ion batteries.

  The present invention provides a new type of silicon-containing lithium lanthanum titanate composite solid electrolyte material and a method for producing the same. The inventor of the present invention, in the silicon-containing lithium lanthanum titanate composite solid electrolyte material, when amorphous Si or Si compound is present at the grain boundary between lithium lanthanum titanate crystal particles, the grain boundary conductivity is remarkable. Therefore, the present inventors have found that the total electrical conductivity is improved and have completed the present invention.

That is, the silicon-containing lithium lanthanum titanate composite solid electrolyte material of the present invention has a chemical formula of Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) between lithium lanthanum titanate crystal particles (1). Amorphous Si or Si compounds are present in the grain boundaries. The presence of this amorphous Si or Si compound remarkably improves the grain boundary conductivity, thereby improving the total conductivity.

  Moreover, it is preferable that mass ratio with respect to lithium lanthanum titanate (LLTO) is 0.27%-1.35% based on conversion in Si, and content of the Si or Si compound. Thereby, improvement in grain boundary conductivity can be realized with certainty.

  The present invention employs a wet chemical method to introduce the amorphous Si or Si compound (2) into the grain boundary. This wet chemical method uses an inexpensive organosilicic compound as an additive. In addition to the lithium lanthanum oxide solid electrolyte material, the mass ratio of silicon to lithium lanthanum titanate (when silicon is a Si compound, the mass ratio based on conversion in Si) is 0.27% to 1.35%. In this case, the silicon-containing lithium lanthanum titanate composite solid electrolyte material can be produced by sintering. Moreover, as an organosilicon compound to be used, for example, tetraethoxysilane, tetramethoxysilane and the like are used, but are not limited thereto.

Furthermore, in the silicon-containing lithium lanthanum titanate composite solid electrolyte material of the present invention, the Si compound preferably contains a Si compound containing SiO ₂ and / or Li ions.

  In the present invention, the Si or Si compound is preferably present as an amorphous nano-high silicon layer. It has been discovered that the presence of Si or Si compounds in the amorphous nano-high silicon layer significantly improves the grain boundary conductivity, and thus improves the overall conductivity.

On the other hand, in the present invention, Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is added to the silicon precursor solution, followed by heating and drying, and then Li _3x La _{2 / 3-x} TiO. _{The present} invention provides a method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material characterized by pelletizing and sintering ₃ . Moreover, in the above production method of the present invention, the silicon precursor solution is blended so that the mass ratio with respect to lithium lanthanum titanate is 0.27% to 1.35% based on conversion with Si. In the production method, the sintering temperature is 1100 to 1400 ° C, more preferably 1200 to 1400 ° C. The sintering time of the sintering is 1 to 10 hours, more preferably 2 to 10 hours, and still more preferably 2 to 8 hours. The heating temperature is 50 to 250 ° C, preferably 80 to 250 ° C, more preferably 80 to 200 ° C, still more preferably 120 to 200 ° C, and the heating time is 1 to 5 ° C. It is time, and 2 to 5 hours is more preferable.

Furthermore, the flow of the process implemented by this invention is performed by the following step.
(1) Preparation of LLTO raw material powder Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is prepared using a solid phase method or a sol-gel method, and the raw material powder is dispersed in ethanol. Suspension a is obtained and prepared for use.
(2) Preparation of catalyst Water, ethanol, and ammonia water are blended based on a certain volume ratio to prepare a mixed solution b.
(3) Preparation of silicon precursor solution An organosilicon compound as a silicon raw material is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 50-250 degreeC for 1 to 5 hours.
(6) Drying Dry at 10 to 100 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet, it is sintered at a high temperature of 1100 to 1400 ° C. for 1 to 10 hours to obtain a composite solid electrolyte material.

  For example, tetraethoxysilane, tetramethoxysilane, or the like is used as the organosilicon compound used in the above step (3), but is not limited thereto.

  When the solid electrolyte material produced by the above method was measured by electrochemical impedance spectroscopy, it was found that the grain boundary conductivity was clearly improved. At this time, energy dispersive X-ray spectroscopy (EDX) and transmission type were found. From the characteristics of the electron microscope (TEM), it was found that silicon was present at the grain boundary, and when observed by X-ray diffraction (XRD) and transmission electron microscope (TEM), the silicon present at the grain boundary was It is possible to confirm that it is amorphous.

  The beneficial effects of the present invention are as follows. That is, the LLTO composite solid electrolyte material of the present application has a clear conductivity improvement effect compared to other solid electrolytes and experimental methods that increase the sintering temperature to improve the electrical conductivity, and the experimental process is simple. Is easy to operate and greatly shortens the experimental period, lowers the synthesis temperature, and reduces energy consumption and production costs.

FIG. 1 is a schematic view of an LLTO composite solid electrolyte material according to the present invention. FIG. 2 is a scanning electron micrograph of the surface of a sintered sample in the present invention. FIG. 3 is a diagram showing a high-angle scattering dark field (HAADF) of a sintered sample according to the present invention by a scanning transmission electron microscope (STEM). FIG. 4 is an energy dispersive X-ray spectroscopic analysis (EDX) for the linear region in FIG. FIG. 5 is an X-ray diffraction diagram of a sintered sample in the present invention. FIG. 6 is an observation view of a sintered sample according to the present invention by a transmission electron microscope (TEM). FIG. 7 is a change rule of room temperature conductivity of the composite LLTO solid electrolyte when the silicon content is different in the present invention.

The present invention provides a silicon-containing lithium lanthanum titanate LLTO composite solid electrolyte material and a method for producing the same. As shown in FIG. 1, the present invention mainly includes an amorphous material at a grain boundary between crystal grains 1 that is lithium lanthanum titanate (Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16)). Si or Si compound 2 is present. The presence of this amorphous Si or Si compound remarkably improves the grain boundary conductivity, thereby improving the total conductivity. Further, the content of this Si or Si compound is preferably 0.27% to 1.35% by weight based on the conversion in Si, with respect to the lithium lanthanum titanate. Improvements can be realized reliably.

  The present invention employs a wet chemical method to realize the introduction of this amorphous Si or Si compound 2 into the grain boundary. This wet chemical method uses an inexpensive organosilicic compound as an additive to form lithium titanate. In addition to the lanthanum solid electrolyte material, when the silicon content is 0.27% to 1.35% by mass ratio to the lithium lanthanum titanate, the silicon-containing lithium lanthanum titanate composite is obtained by sintering. It is possible to obtain and obtain a solid electrolyte material. Moreover, as an organosilicon compound to be used, for example, tetraethoxysilane, tetramethoxysilane and the like are used, but are not limited thereto.

Furthermore, in the silicon-containing lithium lanthanum titanate composite solid electrolyte material of the present invention, the Si compound contains SiO ₂ and / or the Si compound further contains a Si compound containing Li ions. preferable.

  In the present invention, the Si or Si compound is preferably present as an amorphous nano-high silicon layer. It has been discovered that the presence of Si or Si compounds in the amorphous nano-high silicon layer significantly improves the grain boundary conductivity, and thus improves the overall conductivity.

On the other hand, in the method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material of the present invention, Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is added to the silicon precursor solution and heated. After drying, Li _3x La _{2 / 3-x} TiO ₃ is pelletized and sintered. Furthermore, in the above production method of the present invention, the silicon precursor solution is blended so that the mass ratio with respect to lithium lanthanum titanate is 0.27% to 1.35% based on conversion in Si. preferable.

Furthermore, the flow of the process implemented by this invention is performed by the following step.
(1) Preparation of LLTO raw material powder Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is prepared using a solid phase method or a sol-gel method, and the raw material powder is dispersed in ethanol. Suspension a is obtained and prepared for use.
(2) Preparation of catalyst Water, ethanol, and ammonia water are blended based on a certain volume ratio to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution An organosilicon compound (for example, tetraethoxysilane, tetramethoxysilane, etc.) is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 50-250 degreeC for 1 to 5 hours.
(6) Drying Dry at 10 to 100 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet, it is sintered at a high temperature of 1100 to 1400 ° C. for 1 to 10 hours to obtain a composite solid electrolyte material.

  For example, tetraethoxysilane, tetramethoxysilane, or the like is used as the organosilicon compound used in the above step (3), but is not limited thereto.

  Hereinafter, the present invention will be further described by listing examples in which the amount of added Si is changed and comparative examples in which no Si is added.

  1. First embodiment: Embodiment in which tetraethoxysilane is used as an organosilicon compound and the Si content is changed.

<Comparative example 1>
(1) Preparation of LLTO raw material powder Li _0.35 La _0.55 TiO ₃ is prepared for use by using a solid phase method or a sol-gel method.
(2) Sintering After the powder is pressed into a sheet, it is sintered at a high temperature of 1400 ° C. for 2 hours to obtain a composite solid electrolyte material.

From the characteristics of the solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was not present at the grain boundary. When this electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.33 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.34 × 10 ⁻⁴ S / cm.

<Example 1>
(1) Preparation of LLTO raw material powder Li _0.47 La _0.51 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 80 ml of water, 320 ml of ethanol, and 800 ml of aqueous ammonia are blended to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 0.2 g of tetraethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 250 degreeC for 3 hours.
(6) Drying Dry at 100 ° C. to obtain a composite powder.
(7) Sintering After pressing the composite powder into a sheet, it is sintered at a high temperature of 1100 ° C. for 10 hours to obtain a composite solid electrolyte material.

From the characteristics of the solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The Si content is 0.27% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.40 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.42 × 10 ⁻⁴ S / cm.

<Example 2>
(1) Preparation of LLTO raw material powder Li _0.47 La _0.51 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 80 ml of water, 240 ml of ethanol, and 400 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of silicic precursor solution 0.5 g of tetraethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 200 degreeC for 1 hour.
(6) Drying Dry at 90 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet, it is sintered at a high temperature of 1200 ° C. for 8 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The content of Si is 0.67% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.76 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 1.14 × 10 ⁻⁴ S / cm.

<Example 3>
(1) Preparation of LLTO raw material powder Li _0.35 La _0.55 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 20 ml of water, 80 ml of ethanol and 160 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 0.8 g of tetraethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 120 degreeC for 2 hours.
(6) Drying A composite powder is obtained by drying at 60 ° C.
(7) Sintering After pressing the composite powder into a sheet, it is sintered at a high temperature of 1350 ° C. for 6 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The content of Si is 1.08% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.89 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 1.32 × 10 ⁻⁴ S / cm.

<Example 4>
(1) Preparation of LLTO raw material powder Li _0.35 La _0.55 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 10 ml of water, 60 ml of ethanol, and 50 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 1 g of tetraethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 80 degreeC for 5 hours.
(6) Drying Dry at 30 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet shape, it is sintered at a high temperature of 1400 ° C. for 2 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The Si content is 1.35% by mass with respect to lithium lanthanum titanate. Further, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.59 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.78 × 10 ⁻⁴ S / cm.

  A method for confirming the presence of amorphous silicon at the grain boundary between crystal grains will be described with an example as follows.

  1) First, taking the composite solid electrolyte material sample obtained in Example 3 (the content of Si is 1.08% by mass with respect to lithium lanthanum titanate) as an example, the sample scan shown in FIG. Based on high-angle scattering dark field (HAADF) by transmission electron microscope (STEM), discovers the presence of substances with different compositions at grain boundaries;

  2) Next, the presence of silicon was measured in the scanned grain boundary region by performing energy dispersive X-ray spectroscopy (EDX) on the linear region in FIG. 3 (see FIG. 4).

  Thereby, it was confirmed that Si was present at the grain boundary of the obtained composite solid electrolyte material.

  3) Further, by performing X-ray diffraction (XRD) on the composite solid electrolyte materials obtained in the above comparative example and Examples 1-4, as shown in the X-ray diffraction diagram of FIG. From the fact that no diffraction peak was detected, it was proved that silicon exists as an amorphous substance.

  4) Further, as shown in FIG. 6, the composite solid electrolyte material sample obtained in Example 3 (Si / LLTO is 1.08% by mass) is observed with a transmission electron microscope (TEM). It was confirmed that amorphous was present in the boundary region.

  As can be seen from the above detection, amorphous Si is present at the grain boundaries between the crystal grains of the lithium lanthanum titanate of the present invention.

Further, based on the composite solid electrolyte materials obtained in the above comparative example and Examples 1 to 4, as shown in FIG. 7, the relationship between the Si content and the conductivity (ie, depending on the Si content) Thus, a graph showing the change in conductivity at room temperature of the composite solid electrolyte material was prepared. As can be clearly seen from FIG. 7 and the data in the above comparative examples and each example, when Si is not included, the grain boundary conductivity is only 0.34 × 10 ⁻⁴ S / cm, and the total conductivity is Slightly 0.33 × 10 ⁻⁴ S / cm; when the Si content reaches 0.27 mass% (Si / LLTO, the same applies below), the grain boundary conductivity is 0.42 × 10 ⁻⁴ S / cm The total conductivity is 0.40 × 10 ⁻⁴ S / cm, and as the Si content increases, both the grain boundary conductivity and the total conductivity are remarkably improved, and the Si content is 1. When it reaches 08 mass%, the grain boundary conductivity reaches a peak value of 1.32 × 10 ⁻⁴ S / cm, and the total conductivity also reaches a peak value of 0.89 × 10 ⁻⁴ S / cm. When the Si content is further increased to 1.35% by mass, the grain boundary conductivity decreases to 0.78 × 10 ⁻⁴ S / cm and the total conductivity decreases to 0.59 × 10 ⁻⁴ S / cm. This grain boundary conductivity and the total conductivity are clearly improved as compared with the case where no is contained. As can be seen from the above, when the Si content is in the range of 0.27 to 1.35% by mass, the total conductivity of the LLTO composite solid electrolyte material is clearly improved.

  2. Second embodiment: an embodiment in which tetramethoxysilane is an organosilicon compound and the Si content is changed.

  In the above examples, it was explained that tetraethoxysilane was used as the organosilicon compound. Hereinafter, the use of tetramethoxysilane as the organosilicon compound will be described.

<Comparative example 2>
(1) Preparation of LLTO raw material powder Li _0.15 La _0.61 TiO ₃ is prepared for use by using a solid phase method or a sol-gel method.
(2) Sintering After the powder is pressed into a sheet, it is sintered at a high temperature of 1400 ° C. for 2 hours to obtain a composite solid electrolyte material.

From the characteristics of the solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was not present at the grain boundary. When this electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.33 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.34 × 10 ⁻⁴ S / cm.

<Example 5>
(1) Preparation of LLTO raw material powder Li _0.15 La _0.61 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 80 ml of water, 320 ml of ethanol, and 800 ml of aqueous ammonia are blended to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 0.085 g of tetramethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 250 degreeC for 3 hours.
(6) Drying Dry at 100 ° C. to obtain a composite powder.
(7) Sintering After pressing the composite powder into a sheet, it is sintered at a high temperature of 1100 ° C. for 10 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The Si content is 0.27% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.40 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.42 × 10 ⁻⁴ S / cm.

<Example 6>
(1) Preparation of LLTO raw material powder Li _0.06 La _0.65 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 80 ml of water, 240 ml of ethanol, and 400 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 0.212 g of tetramethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 200 degreeC for 1 hour.
(6) Drying Dry at 90 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet, it is sintered at a high temperature of 1200 ° C. for 8 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The content of Si is 0.67% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.76 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 1.14 × 10 ⁻⁴ S / cm.

<Example 7>
(1) Preparation of LLTO raw material powder Li _0.45 La _0.51 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 20 ml of water, 80 ml of ethanol and 160 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of silicic precursor solution 0.339 g of tetramethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 120 degreeC for 2 hours.
(6) Drying A composite powder is obtained by drying at 60 ° C.
(7) Sintering After pressing the composite powder into a sheet, it is sintered at a high temperature of 1350 ° C. for 6 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The content of Si is 1.08% by mass with respect to lithium lanthanum titanate. Furthermore, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.89 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 1.32 × 10 ⁻⁴ S / cm.

<Example 8>
(1) Preparation of LLTO raw material powder Li _0.3 La _0.56 TiO ₃ is prepared using a solid phase method or a sol-gel method, and 10 g of raw material powder is dispersed in ethanol to obtain a suspension a for use. Prepare for.
(2) Preparation of catalyst 10 ml of water, 60 ml of ethanol, and 50 ml of aqueous ammonia are mixed to prepare a mixed solution b.
(3) Preparation of Silica Precursor Solution 0.424 g of tetramethoxysilane is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 80 degreeC for 5 hours.
(6) Drying Dry at 30 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet shape, it is sintered at a high temperature of 1400 ° C. for 2 hours to obtain a composite solid electrolyte material.

From the characteristics of the composite solid electrolyte material obtained by the above method by energy dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM), it was confirmed that silicon was present at the grain boundaries. Further, when observed with X-ray diffraction (XRD) and a transmission electron microscope (TEM), it was confirmed that silicon existing at the grain boundaries was amorphous. The Si content is 1.35% by mass with respect to lithium lanthanum titanate. Further, when the obtained solid electrolyte material is measured by electrochemical impedance spectroscopy, the total conductivity reaches 0.59 × 10 ⁻⁴ S / cm, and the grain boundary conductivity reaches 0.78 × 10 ⁻⁴ S / cm.

  As described above, with respect to the composite solid electrolyte materials obtained in Examples 5 to 8 above, a method for determining that amorphous silicon is present at the grain boundaries between the crystal grains in the first embodiment, and When measured in the same manner, the same result as in the first embodiment, that is, it can be obtained that amorphous silicon exists at the grain boundaries between the crystal particles of the obtained composite solid electrolyte material.

  As can be seen from the comparison between Examples 5 to 8 and Comparative Example 2 in the second embodiment, amorphous Si (or Si compound) is present at the grain boundaries as in the first embodiment. In general, the solid electrolyte material exhibits a relatively high conductivity because the amorphous Si or Si compound existing at the grain boundary plays a role of improving the electron conduction function between the crystal grains. Conventionally, it solves the low grain boundary conductivity that has the greatest influence on the total conductivity, so that the solid electrolyte material can be applied to a wide range of lithium batteries. Moreover, in the second embodiment in which tetramethoxysilane is used as the organosilicon compound, when the Si content is in the range of 0.27 to 1.35% by mass, the total conductivity of the composite solid electrolyte material is Remarkably improved.

Claims (14)

A silicon-containing lithium lanthanum titanate composite solid electrolyte material having a chemical formula of Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) and amorphous at the grain boundaries between lithium lanthanum titanate crystal particles A silicon-containing lithium lanthanum titanate composite solid electrolyte material, wherein Si or a Si compound is present.   2. The silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 1, wherein the Si or Si compound has a mass ratio with respect to lithium lanthanum titanate of 0.27% to 1.35% based on conversion with Si. 3. The silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 1, wherein the Si compound contains a Si compound containing SiO ₂ and / or Li ions.   4. The silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 1, wherein the Si or Si compound is present as an amorphous nano-high silicon layer. 5. A method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material, wherein Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is added to a silicon precursor solution and dried by heating. A method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material that is pelletized and sintered.   6. The silicon-containing lithium lanthanum titanate composite solid according to claim 5, wherein the silicon precursor solution is blended so that the mass ratio with respect to lithium lanthanum titanate is 0.27% to 1.35% based on conversion with Si. Manufacturing method of electrolyte material.   The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 5 or 6, wherein the sintering temperature is 1100 to 1400 ° C.   The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 7, wherein the sintering temperature is 1200 to 1400 ° C.   The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to any one of claims 5 to 8, wherein the sintering time is 1 to 10 hours.   The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 9, wherein the sintering time is 2 to 10 hours.   The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 10, wherein the sintering time is 2 to 8 hours. The method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to claim 5 or 6, wherein the following steps are performed.
(1) Preparation of LLTO raw material powder Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) is prepared using a solid phase method or a sol-gel method, and the raw material powder is dispersed in ethanol. Suspension a is obtained and prepared for use.
(2) Preparation of catalyst Water, ethanol, and ammonia water are blended based on a certain volume ratio to prepare a mixed solution b.
(3) Preparation of silicon precursor solution An organosilicon compound is weighed and dispersed in ethanol to obtain a solution c.
(4) Preparation of mixed solution After the suspension a and the mixed solution b are mixed, the solution c is dropped into the mixed solution and stirred uniformly.
(5) Heating reaction The stirred liquid mixture is heated at 50-250 degreeC for 1 to 5 hours.
(6) Drying Dry at 10 to 100 ° C. to obtain a composite powder.
(7) Sintering After the composite powder is pressed into a sheet, it is sintered at a high temperature of 1100 to 1400 ° C. for 1 to 10 hours to obtain a composite solid electrolyte material.   The silicon-containing lithium lanthanum titanate according to claim 12, wherein the organosilicon compound to be weighed is at least one of tetraethoxysilane and tetramethoxysilane in the step of preparing the silicon precursor solution. A method for producing a composite solid electrolyte material.   In the catalyst preparation step, water, ethanol, and aqueous ammonia are mixed based on a mixing ratio in a volume ratio of 1: 2: 2 to 1: 4: 10 to prepare a mixed solution b. Item 13. A method for producing a silicon-containing lithium lanthanum titanate composite solid electrolyte material according to Item 12.

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